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SK83 (Mechanical) (OP)
9 Feb 12 14:16
I'm currently looking at the loads subjected on the Main Bearing in a Wind Turbine. I have completed the calculations as per IEC 61400. This has allowed me to calculate the Axial load, Bending moment and torque of the shaft.

I have to calculate the Radial Load, which I have done using the equation RL = Torque/Shaft Radius. However the figure I am equating is a radial load of 3MN, which seems far to high.

Is this the correct equation to use?

If not, what should I be doing?
rb1957 (Aerospace)
9 Feb 12 14:23
i don't know your code, so this could be gibberish, but anyways ...

i suspect torque of the shaft is the torque created by the blades of the wind-mill which would be reacted by the torque required to drive the generator at the other end of the shaft.

radial load as i see it would have something to do with the gyroscopic effects of the spinning blades, and an off-axis wind condition.  
SK83 (Mechanical) (OP)
9 Feb 12 14:53
Thanks for your reply, you are correct, the shaft torque = rotor torque.

calculated as;

(rated power x 30)/(rotor speed x pi x 0.8)

where Power = 1500x10^3 watts and Rotor speed = 20.5 r/min

=> Torque = 873411.27 Nm

My understanding is to convert this to Radial Load, I would use;

T = radius x load => Load = T/radius.

If my shaft radius is 0.285m

This equates to Radial load of 3.06 MN.

Which I feel is incorrect. Therefore I suspect I'm using the wrong equation.

 
rb1957 (Aerospace)
9 Feb 12 15:52
yes, i agree ... why would the prop torque be reacted on the surface of the shaft ?  unless you were applying a brake ?

won't the torque travel along the shaft from the prop plane to the generator ?
btrueblood (Mechanical)
9 Feb 12 15:59
It's good that you use x for the multiplication symbol there.  The right equation is (in vector form)

Torque = F x r

where the bold indicates vectors, and x is the vector cross product.

Dunno how you would create a moment (torque) with a radially directed force...a tangentially directed force on the other hand...
rb1957 (Aerospace)
9 Feb 12 16:01
is it just me or is this looking like a student post ?
SK83 (Mechanical) (OP)
9 Feb 12 16:23
rb1957 - I wasn't aware asking for advice on a problem  was against any forum rules, student or not. I was looking for guidance(or tip) in what direction to follow.

The question I posed is a small part of a far larger project.
 
rb1957 (Aerospace)
9 Feb 12 16:48
if you're a student, asking a question about an assignment, you're a "student post".

you could be a student, working, like a co-op, asking a question from the real world ... just doesn't look like it.

i note that you haven't answered the question, why react the prop torque at the side of the shaft (unless you're applying a brake) ?
SK83 (Mechanical) (OP)
9 Feb 12 17:07
I'm completing a project/study into the viability of implementing a different type of main bearing used within a wind turbine, which is currently a rolling element bearing. I work F/T and study P/T.

The main bearing is positioned approx. 1 metre from the rotor, and is subjected to loads caused by the Rotor. Those being axial, and radial.

The stalling point I have is working out the Radial load on the bearing.

I may have a major misunderstanding with the relationship between Torque and Load, which I expressed earlier.
Helpful Member!  patdh1028 (Mechanical)
9 Feb 12 17:34
Radial loading is a condition where the force passes through the central axis of the cross-section. It's a radial line. Torque does not directly factor into this load, at least not the torque spinning the shaft.

There are two conditions contributing to a radial load. The first is the static moment and load of the rotor, which is hanging on a shaft 1 meter from the main bearing. Simple beam equations will suffice to find those loads.

The second condition effecting radial loading is shaft deflection and/or rotor imbalance; as the center of mass of the rotor shifts away from  an ideal central rotation axis, there will be axial loading equal to m*r*(rotation speed)^2, where r is the distance from the COM to the center of rotation and m is the rotor mass.

I think that is what you are looking for. Shaft torque does not load the bearing significantly, as long as the bearing is in working order.
SK83 (Mechanical) (OP)
9 Feb 12 17:50
patdh1028 - Thanks. That's now clear. It's obvious I did have a misunderstanding.  
vpl (Nuclear)
9 Feb 12 17:50
Sk83

Since you just joined and you stated that you weren't aware that "asking for advice on a problem  was against any forum rules, student or not," you might want to read the FAQ in my tag line.   

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

dhengr (Structural)
9 Feb 12 18:16
I think Patdh1028 has it right.  But don't forget this is a simple beam with a 1m cantilever loaded with the rotor mass and dynamics at the canti. tip.  The shaft is supported by the bearing and then continues beyond the bearing to a gear box or coupling of some sort which likely contributes additional loading to the bearing, from the back span of the shaft.  The point being that the rotor might not contribute the only radial load to the bearing.  And, in a static situation that radial load on the bearing will be at 6 o'clock when looking at the end of the shaft.  But, the radial load may be somewhat higher when running, and at be 4 or 8 o'clock approx., due to friction and dynamic affects, and the like.
 
SnTMan (Mechanical)
9 Feb 12 18:26
Shall precession effects be included?

Regards,

Mike
Tmoose (Mechanical)
9 Feb 12 20:53
what does the turbine drive?  If there is a gear train things (loading) might be different than if the generator is direct coupled or integral.
tbuelna (Aerospace)
10 Feb 12 17:19
SK83,

I would assume your HAWT drivetrain is the typical 3 point mount with the fwd rotor shaft bearing being a duplex spherical roller and the aft bearing being a pair of cylindrical rollers supporting the primary planetary stage carrier within the gearbox. And the rotor shaft would be rigidly coupled to the gearbox primary stage planet carrier using a hydraulic shrink coupling, and the gearbox housing is mounted on a pair of horizontal trunnion shafts.

In this case, the only significant source of radial load on the forward rotor shaft bearing is the mass of the rotor hub, shaft and blades.  On a typical 1.5MW utility scale turbine, these components' combined weight can easily exceed 30 tons.  

The forward duplex spherical roller bearing also would be subject to axial loads, due to the blade thrust forces.  However, by far the most significant forces the rotor shaft bearings are subject to are the out-of-plane rotor moments, due to variations in wind velocity across the rotor disc creating asymmetric blade lifts.

Here's a good reference on HAWT rotor shaft bearings:  http://www.timken.com/en-us/solutions/windenergy/Documents/TDICRBvsSRBSRB.pdf

Hope that helps.
Terry

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